This invention relates generally to electric generators, and more particularly, to methods and apparatus for controlling an air gap between a rotor and a stator in a wind-powered turbine generator.
Recently, wind turbines have received increased attention as an environmentally safe and relatively inexpensive alternative energy source. With this growing interest, considerable efforts have been made to develop wind turbines that are reliable and efficient.
Generally, a wind turbine includes a plurality of blades coupled to a rotor through a hub. The rotor is mounted within a housing or nacelle, which is positioned on top of a tubular tower or base. Utility grade wind turbines (i.e., wind turbines designed to provide electrical power to a utility grid) can have large rotors (e.g., 30 or more meters in diameter). Blades on these rotors transform wind energy into a rotational torque or force that drives the rotor of one or more generators, rotationally coupled to the rotor. The rotor is supported by the tower through a bearing that includes a fixed portion coupled to a rotatable portion. The bearing is subject to a plurality of loads including a weight of the rotor, a moment load of the rotor that is cantilevered from the bearing, asymmetric loads, such as, horizontal wind shears, yaw misalignment, and natural turbulence
In the generator, rotor components and stator components are separated by an airgap. During operation, a magnetic field generated by permanent magnets and/or wound magnets mounted on the rotor passes through the airgap between the rotor to the stator. The passage off the magnetic field through the airgap is at least partly dependent on the uniformity of the airgap. Asymmetric and/or transient loads on the rotor may be introduced through the blades. Such loads are channeled from the rotor to the wind turbine base through the bearing and may tend to deflect structural components of the rotor in the load path such that the airgap distance is reduced and/or made non-uniform. Wind turbine components may be fabricated to withstand such loads. However, the size and weight disadvantage of those components make their use economically prohibitive. Additionally, the substantial structure needed to control the airgap would use up valuable Hub-Access space needed to install and service systems such as Pitch-Control and other devices.